Wide-angle planar-beam antenna adapted for conventional or doppler scan using dielectric lens

ABSTRACT

An antenna involving a plurality of vertical-array-excited parallel-plate coordinate converters feeding a dielectric lens in the shape of a partial toroid. Each corresponding element of the array feeding each parallel-plate coordinate converter is fed in parallel through a wave guide feed arrangement from a Doppler line feed or phased array feed. The radiated beam shape tends to hold its focus and, therefore, has uniform width in elevation over the full azimuth beam width at all useful elevation beam positions.

United States Patent [1 1 Nemit WIDE-ANGLE PLANAR-BEAM ANTENNA ADAPTEDFOR CONVENTIONAL OR DOPPLER SCAN USING DIELECTRIC LENS [75] Inventor:Jeffrey T. Nemit, Canoga Park,

Calif.

[73] Assignee: International Telephone and Telegraph Corporation, NewYork, N.Y.

[22] Filed: Dec. 18, 1972 [21] Appl. No.: 316,240

[52] U.S. Cl. 343/754, 343/854 [51] Int. Cl. H0lq 19/06, HOlq 3/26 [58]Field of Search ..343/754, 854, 876, 106 D,

[56] References Cited UNITED STATES PATENTS 2,720,589 10/1955 Proctor..343/854 DOPPLER L//VE FEED [ Feb. 26, 1974' Horst 343/754 Sferrazza343/754 Primary ExaminerEli Lieberman Assistant ExaminerWm. H. PunterAttorney, Agent, or FirmW. T. ONeill [57] ABSTRACT An antenna involvinga plurality of vertical-arrayexcited parallel-plate coordinateconverters feeding a dielectric lens in the shape of a partial toroid.Each corresponding element of the array feeding each parallel-platecoordinate converter is fed in parallel through a wave guide feedarrangement from a Doppler line feed or phased array feed. The radiatedbeam shape tends to hold its focus and, therefore, has uniform width inelevation over the full azimuth beam width at all useful elevation beampositions.

6 Claims, 4 Drawing Figures PATENTEUFEBZBISM DOPPLER L/A/E FEEDHOE/ZOA/TQL FEEDS TOT/4L 142 WIDTH OF 554M WIDE-ANGLE PLANAR-BEAMANTENNA ADAPTED FOR CONVENTIONAL OR DOPPLER SCAN USING DIELECTRIC LENSCROSS REFERENCE TO RELATED APPLICATIONS U.S. Pat. application Ser. No.272,451 filed July 17, 1972, entitled A Technique for Generating PlanarBeams from a Linear Doppler Line Source or Linear Phased Array (JeffreyT. Nemit, inventor) contains disclosure pertinent to the description ofthe present invention. Accordingly, the disclosure of that applicationis incorporated herein by reference as though fully set forth herein.

BACKGROUND OF THE INVENTION 1. Field of the Invention The inventionrelates to scannable antennas and, in particular, to antenna systems forair navigation and guidance systems requiring vertical angledetermination.

2. Description of the Prior Art The above-referenced U.S. patentapplication is itself descriptive of an improvement in antenna systemsknown and used in connection with the so-called Doppler-scan technique.The related prior art preceding that invention is typically describedand referenced in U.S. Pat. Nos. 3,613,096 and 3,670,338. U.S. Pat.application Ser. No. 210,669, filed Dec. 22, 1971, is also a usefulreference for background information in describing the state of theprior art. Those references also are useful in understanding the natureof the problems encountered in Doppler-scan systems, for example. Theutility of the present invention is particularly great in connectionwith systems of those types.

U.S. Pat. application Ser. No. 272,451 (abovereferenced) describes adevice employing a circular aperture, parallel-plate wave guideconverter excited by a linear Doppler-scan array or alternatively by anelectronic-scan phased array or the like. The purpose of thatparallel-plate structure, as is fully described in that application,Ser. No. 272,45 1 is the conversion of fundamentally conical-coordinatebeams to planarcoordinate beams. That device is employed as an elementin the novel combination of the present invention as hereinafterdescribed.

In U.S. Pat. No. 3,653,057, entitled Simplified Multi-Beam CylindricalArray Antenna with Focused Azimuth Patterns Over a Wide Range ofElevation Angles," a system for tailoring the beam shape of a scanningantenna for wide-angle performance in the nonscanning coordinate isdescribed. That device uses multiple beams to achieve the desiredeffect, and while satisfactory in typical L-band systems, is relativelyinefficient at C-band and above.

The manner in which the present invention builds on the techniques ofthe prior art and the extent to which it affects improvements thereoverwill be evident as this description proceeds.

SUMMARY OF THE INVENTION The combination of the present inventioninvolves the use of a plurality of coordinate-converting parallelpartialtoroid. The lens antenna arrangement produced is vertically orientedfunctionally; i.e., it is intended to produce vertically scannable beamshaving predetermined azimuth characteristics which remain substantiallyconstant over the useful elevation scanning angles. The referenced U.S.Pat. No. 3,653,057, on the other hand, is horizontally oriented by thesame criterion.

It may be said that the general objective of the present invention isthe production of a basically vertically oriented antenna (although itsuse as a horizontally oriented device is not precluded) to formhorizontal fan beams of substantial azimuth angular width, the saidantenna being adapted for scanning in elevation without deterioration ofthe focus uniformity of the beams at various elevation beam positions.Use of a simple linear array does not accomplish this objective becauseit beams have a conical shape when scanned. The circular parallel-platewave guide described in the aforementioned U.S. Pat. application Ser.No. 272,451, used by itself, provides the required planar-beam forconsistency with coordinate systems utilized in the so-calledDoppler-scan air navigation and guidance systems. However, the use ofthat circular parallel-plate wave guide arrangement, as described in thereference, is limited in wide angle coverage in the nonscanningcoordinate, due to defocusing which distorts the elevation beam width atwide azimuth angles.

If it is imagined that an observer from a distance looks down the beamtoward this antenna and is able to see the cross-sectional shape of thetotal beam, that beam would appear somewhat in the shape of a dogbone.This is because defocusing at azimuth angular extremes tends to fattenthe beam in the elevation coordinate at those azimuth extremes. Thepresent invention, which is particularly adapted to use a radar C- bandoperation and above, employs an optical technique to provide therequired wide-angle beam in azimuth in an arrangement affording theplanar coordinates effected by the aforementioned Ser. No. 272,451device as a feed, while providing a more idealized focusing to eliminatethe so-called dogbone effect.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a pictorial view of anantenna arrangement in accordance with the present invention.

FIG. 2 is a top view taken along the section line AA of FIG. 1.

FIG. 3 is an expanded pictorial view showing the details of the feedarrangements for the plural parallelplate converters of the combination.

FIGS. 4(a) and (b) are respective beam crosssections for prior art andpresent systems.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, apictorial view of the antenna assembly according to the presentinvention is presented. The lens 18 is partially cut away to show theparallel-plate coordinate converters 13, 14, 15, 16 and 17. Thoseparallel-plate wave guide converters are excited in parallel from acommon Doppler-line feed 10 and a plurality of wave guide couplingsections 19, 20, 21, 22 and 23. The semi-circular apertures of theseparallel-plate wa-ve guides act as individual feeds operating into atoroidal shape lens of the general Luneburg type. The effect of the lensin combination with these apertures is to produce the correct ringphasefor focusing in elevation at a different azimuth angle. Thus, it may besaid that the azimuth beam is composed of a plurality of overlappingindividual narrower beams, and here the general theory of forming anazimuth beam builds from the aforementioned U.S. Pat. No. 3,653,057.Accordingly, it may be said that each of the vertical parallel-platewave guide apertures acts as a feed to a lens which produces a focusedbeam at discrete and different azimuth angles for each of theparallel-plate devices. The combination of all those beams produces thewide angle beam in azimuth with substantially constant elevation width.Looking ahead to FIG. 4, this effect is illustrated. As hereinaboveindicated, the observer looking down the beam sees a dogbone beam shape,per FIG. 4(a), when the parallel-plate device is used a lone as setforth in the aforementioned U.S. Pat. application Ser. No. 272,451. InFIG. 4(a), the elevation dimension of the scannable beam 38 is minimumat 35 and broadens out at 36 and 36a to give the so-called dogboneshape. According to the present invention, on the other hand, theplurality of individual beams making up the azimuth fan shape aretypically 39 and 40, etc., in FIG. 4(b). Those individual beamscorrespond to the radiations of 13, 14, etc., from FIG. 1, as focused bythe lens 18 in accordance with the further description hereinafter.

A relative dielectric constant of about four for the toroidal lensresults in an optimization of the quadratic and fourth-order azimuthphase errors, thereby achieving nearly constant phase. The insideperimeter of the toroidal lens at 12 is circular, as is the outsideperimeter in two planes viewed at 11.

Referring now to FIG. 2, which is a view looking down in accordance withthe section line AA in FIG. 1, the cross-section of the lens 18 will beseen to be circular. Assuming that the section line illustrated in FIG.1 passes through points 11 and 12, the horizontal wave guide couplingsection 21 will be the one evident in FIG. 2. Its connection to theparallel-plate wave guide converters 13 through 17, as seen in FIG. 2,is typical of the connection of the other wave guide coupling sections19, 20, 22 and 23 at the respective vertical placements. The actualapertures of the individual parallelplate wave guide converters are madeto conform to the shape of the lens. That is, it will be seen from FIG.2 that parallel-plate wave guide apertures of 13 and 14 are chamfered atthe point of contact with the lens as illustrated at 13a and 14a in FIG.2.

Concerning materials for the elements of the present combination, itwill be understood that the parallelplate wave guides, and all otherwave guide parts illustrated, may be made of the common conductivematerials used for wave guide construction. The toroidal lens may beconstructed from a modified cross-linked polyolefin material. Suchmaterial is available under the tradename Custom poly K-Flex, a productmanufactured by Custom Materials, Inc. of Chelmsford, Mass.

Referring now to FIG. 3, the substantially identical parallel-plate waveguide coordinate converters 13, 14, 15, 16 and 17 are as described inthe aforementioned U.S. Pat. application Ser. No. 272,451. It will benoted that the space between the parallel-plates, for example, in 13, isexcited by a vertical array of slot antenna elements 29, 30, 31, 32 and33. The referenced patent application describes how these slots form anarray as part of a conventional scanning or Doppler-scanning source. Thecorresponding slots in each of the other parallel-plate arrangements 14through 17 are all excited in parallel. That is, the distribution waveguide 19 connects to the corresponding slot in each of the otherparallel-plate arrangements as it does at slot 29 within 13. Similarly,the distribution wave guides 20, 21, 22 and 23 connect to the slots 30,31, 32 and 33, respectively, and to the corresponding slots in each ofthe other parallel-plate wave guides 14 through 17. These horizontalfeed distribution wave guides, on the other hand, are themselvesseparately excited, one to a slot from slots 24 through 28,communicating with the Doppler-line feed 10. It will be realized, ofcourse, that the Doppler-line feed 10 could be a conventional scanningarrangement. The slots 24 through 28 are, thus, the scanned orcommutated elements and the corresponding slots within each of theparallel-plate wave guide converters are excited in parallel.

The reference to the lens shape as a partial toroid refers to thegeneral shape depicted in FIG. 1. The segment of the toroid providedmust at least extend around the generally circular aperture of theparallelplate wave guide converters used.

The reference to an axis of the toroid refers generally to a line whichwould extend through the center of the inside perimeter normal to theparallel-plate wave guides. Thus, the axis would pass centrally throughthe hole of the donut.

The inside perimeter of the toroid means the perimeter measured in thecenter of the hole of the donut and the inside perimeter surface meansthe surface of the toroid inside the arbitrary line 34 through thecenter of the toroid section in FIG. 2.

For optimum performance of the antenna arrangement in accordance withthe present invention, the designer may find it desirable to insert amatching section at the interface of each of said parallel plate waveguides with the inside perimeter surface of the toroidal lens; however,this is a matter falling within the ordinary skills of this art.

Modifications and variations within the scope of the present novelcombination will suggest themselves to those skilled in this art, oncethe principles hereof are understood. Accordingly, it is not intendedthat the drawings or this description, which are illustrative andtypical only, should constitute a limitation on the present invention.

What is claimed is:

1. An antenna system for radiating planar beams scannable in a firstangular coordinate and of substantially constant beam width in the sameangular coordinate over a wide range of angles in a second orthogonalangular coordinate, comprising:

a dielectric lens in the shape of a partial toroid havingcircular-shaped inside and outside perimeter surfaces and a full circlecross-sectional shape in a plane containing the axis of said toroid;

a plurality of parallel-plate wave guide feeds coupled to said lensalong a portion of said inside perimeter, said parallel-plate waveguides being normal to the axis of said toroid and spaced in thedirection of said axis, said parallel-plate wave guides further havingtheir apertures abutting the inside surface of said toroid;

a scan feed array including a first linear array of antenna elements;

a plurality of second linear arrays of antenna elements, one within eachof said parallel-plate wave guide feeds;

and a plurality of coupling transmission lines for coupling each elementof said first'linear array in parallel with corresponding elements ineach of said second linear arrays.

2. Apparatus according to claim 1 in which said dielectric lens isdefined as having an approximate dielectric constant of 4.

3. Apparatus according to claim 2 in which said scan feed arraycomprises the elements of a phased array.

4. Apparatus according to claim 2 in which said antenna elements of saidfirst linear array comprise slots in an associated wave guidetransmission line and each of said coupling transmission lines comprisesa wave guide.

5. Apparatus according to claim 4 in which the number of said antennaelements in each of said second linear arrays equals the number of saidelements in said first linear array, there also being an equal number ofsaid coupling transmission lines.

6. Apparatus according to claim 5 in which each of said couplingtransmission lines is coupled to said scan feed array through one ofsaid slots of said first linear array and slots in said couplingtransmission lines are provided coincidental with said correspondingantenna elements of each of said second arrays, whereby said parallelfeed of corresponding elements of said second array is provided.

1. An antenna system for radiating planar beams scannable in a firstangular coordinate and of substantially constant beam width in the sameangular coordinate over a wide range of angles in a second orthogonalangular coordinate, comprising: a dielectric lens in the shape of apartial toroid having circular-shaped inside and outside perimetersurfaces and a full circle cross-sectional shape in a plane containingthe axis of said toroid; a plurality of parallel-plate wave guide feedscoupled to said lens along a portion of said inside perimeter, saidparallelplate wave guides being normal to the axis of said toroid andspaced in the direction of said axis, said parallel-plate wave guidesfurther having their apertures abutting the inside surface of saidtoroid; a scan feed array including a first linear array of antennaelements; a plurality of second linear arrays of antenna elements, onewithin each of said parallel-plate wave guide feeds; and a plurality ofcoupling transmission lines for coupling each element of said firstlinear array in parallel with corresponding elements in each of saidsecond linear arrays.
 2. Apparatus according to claim 1 in which saiddielectric lens is defined as having an approximate dielectric constantof
 4. 3. Apparatus according to claim 2 in which said scan feed arraycomprises the elements of a phased array.
 4. Apparatus according toclaim 2 in which said antenna elements of said first linear arraycomprise slots in an associated wave guide transmission line and each ofsaid coupling transmission lines comprises a wave guide.
 5. Apparatusaccording to claim 4 in which the number of said antenna elements ineach of said second linear arrays equals the number of said elements insaid first linear array, there also being an equal number of saidcoupling transmission lines.
 6. Apparatus according to claim 5 in whicheach of said coupling transmission lines is coupled to said scan feedarray through one of said slots of said first linear array and slots insaid coupling transmission lines are provided coincidental with saidcorresponding antenna elements of each of said second arrays, wherebysaid parallel feed of corresponding elements of said second array isprovided.